1. Field of the Invention
The present invention relates to an apparatus for realizing a secret communication by encrypting and relaying frames in the data link layer.
2. Description of the Related Art
Ethernet has been widely used for purposes ranging from personal use to corporate backbone systems because it realizes high-speed communications such as 10 Mbps, 100 Mbps, and 1 Gbps, and communications equipment such as NICs (Network Interface Cards), hubs, switches, and cables are affordable and easily available.
The Ethernet standard defines the specifications of the physical layer (also referred to as Layer 1) and the data link layer (also referred to as Layer 2) in the OSI (Open Systems Interconnection) reference model. Layer 2 is further divided into two sublayers according to the IEEE (Institute of Electrical and Electronic Engineers) 802.3 standard in which Ethernet was standardized. The sublayer close to Layer 1 is the MAC (Media Access Control) sublayer, and the one close to the network layer (also referred to as Layer 3) is the LLC (Logical Link Control) sublayer. In Layer 2, data is sent and received in units of frames.
Although Ethernet is widely used as described above, the communication itself with Ethernet has not been encrypted. That is, frames sent and received are not encrypted. Thus, when the communication is intercepted, important information is leaked out.
When using a repeater hub, all terminals connected to the same hub can intercept the communication. When using a switching hub, while it is normally impossible to intercept the communication of other terminals, the communication can be easily intercepted by using offensive methods such as ARP (Address Resolution Protocol) spoofing and MAC flooding. For this reason, there has arisen a need for encrypting the Ethernet communication in order to keep communication contents confidential.
The encryption of the Ethernet communication itself is possible by using existing protocols. There are several methods, as described below, and all have problems.
The first method is to combine IPsec, described in nonpatent literature 1, and EtherIP, described in nonpatent literature 2 (the method is also called “EtherIP over IPsec”).
IPsec is an architecture for securing Internet communications, including the technology of encrypting IP (Internet Protocol) packets. EtherIP is a method for realizing the Ethernet communication on the IP. Therefore, the Ethernet communication can be encrypted by using the combination of IPsec and EtherIP.
The second method is to combine the IPsec described in nonpatent literature 1 and L2TPv3, described in nonpatent literature 3. L2TPv3 is a method for transmitting a Layer 2 frame on the IP. Therefore, the Ethernet communication can be encrypted by using the combination of IPsec and L2TPv3.
The third method is to encrypt the MAC sublayer, which is now in preparation and will be standardized as IEEE802.1AE. The Ethernet communication can be encrypted by encrypting the MAC sublayer.
[Nonpatent literature 1]RFC4301 Security Architecture for the Internet Protocolhttp://www.ietf.org/rfc/rfc4301.txt(Access confirmed: Jul. 28, 2006)[Nonpatent literature 2]RFC3378 EtherIP: Tunneling Ethernet Frames in IP Datagramshttp://www.ietf.org/rfc/rfc3378.txt(Access confirmed: Jul. 28, 2006)[Nonpatent literature 3]RFC 3931 Layer Two Tunneling Protocol—Version 3 (L2TPv3)http://www.ietf.org/rfc/rfc3931.txt(Access confirmed: Jul. 28, 2006)
However, the first method has the following problems.    (a) According to EtherIP, an EtherFrame can be transferred only to a specific destination, which results in the limitation to the one-to-one communication topology. That is, the method is only capable of encrypting the communication between a pair of switches having a one-to-one relationship. In a general office LAN (Local Area Network), however, N-to-N communication is often conducted.    (b) Since EtherIP does not perform a bridge operation, it does not learn a MAC address and cannot avoid unnecessary transfers, which generates unnecessary traffic.    (c) It uses a complicated protocol stack comprising IP, IPsec, and EtherIP. The protocol stack is complicated because it comprises these three protocols, IP requires routing, and IPsec requires key exchange. Since the protocol stack is complicated, the configuration definition is also complicated. Accordingly, communications equipment is not easy to operate and maintain.    (d) Since the protocol stack is complicated, realization as hardware is difficult. Meanwhile, realization as software results in a longer processing time. Therefore, it is difficult to realize a Gbps-class function.
The second method also has the same problems as the first method.
The third method also has the following problems.    (e) The switch as the participant of the cryptographic communication needs to be identified, and the key needs to be exchanged with each participating switch using a key exchange protocol. Accordingly, it is not suitable for a topology in which a plurality of switches perform the encrypted communication in an N-to-N relationship since the process becomes too complicated.    (f) The granularity of encryption is in units of physical interfaces. That is, frames sent and received between two specific switches are either all encrypted or all not encrypted. Therefore, it cannot handle a smaller granularity to determine whether or not to perform the encryption for each VLAN (Virtual LAN).